The gender gap is smallest in Washington, D.C. and in New York, the Congressional study said, using an analysis of 2014 census data.

Check out the gender pay gap by state:

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2016 gender pay gap state to state ranking

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Rural US states have biggest gender pay gaps, report shows

51. Louisiana

Gender pay gap: 34.7%

(Ian Dagnall / Alamy)

50. Utah

Gender pay gap: 32.4%

(CountyLemonade/Flickr)

49. Wyoming

Gender pay gap: 31.2%

(Philip Scalia / Alamy)

48. West Virginia

Gender pay gap: 30%

(J. Stephen Conn/Flickr)

47. North Dakota

Gender pay gap: 28.7%

(Tim Evanson/Flickr)

46. Alabama

Gender pay gap: 27.4%

(Danny Hooks / Alamy)

45. Idaho

Gender pay gap: 27.2%

(Philip Scalia / Alamy)

44. Oklahoma

Gender pay gap: 26.5%

(thefixer/Flickr)

43. Montana

Gender pay gap: 25.8%

(John Elk III / Alamy)

42. Michigan

Gender pay gap: 25.5%

(curiousjohn/Flickr)

41. Indiana

Gender pay gap: 24.8%

(ellenm1/Flickr)

40. New Hampshire

Gender pay gap: 24.3%

(cmh2315fl/Flickr)

39. South Dakota

Gender pay gap: 23.8%

(SuperStock / Alamy)

38. Mississippi

Gender pay gap: 23%

(Don Smetzer / Alamy)

37. Kansas

Gender pay gap: 23%

(Jim West / Alamy)

35. Iowa

Gender pay gap: 22.7%

(Ellen Isaacs / Alamy)

34. Missouri

Gender pay gap: 22.6%

(L. Allen Brewer/Flickr)

33. Ohio

Gender pay gap: 22.2%

(sailwings/Flickr)

32. New Mexico

Gender pay gap: 21.9%

(Patrick Ray Dunn / Alamy)

31. Arkansas

Gender pay gap: 21.8%

(Buddy Mays / Alamy)

30. Texas

Gender pay gap: 21.2%

(Ian Dagnall / Alamy)

29. Maine

Gender pay gap: 21.2%

(PHOTOPHANATIC1/Flickr)

28. Nebraska

Gender pay gap: 21.1%

(Ian G Dagnall / Alamy)

27. Wisconsin

Gender pay gap: 21.1%

(Jeff Greenberg 5 / Alamy)

26. Illinois

Gender pay gap: 20.9%

(incamerastock / Alamy)

25. Pennsylvania

Gender pay gap: 20.8%

(dannyfowler/Flickr)

24. Kentucky

Gender pay gap: 20.1%

(toddmundt/Flickr)

23. Virginia

Gender pay gap: 19.8%

(JoeDuck/Flickr)

22. South Carolina

Gender pay gap: 19.8%

(Ellisphotos / Alamy)

21. New Jersey

Gender pay gap: 19.7%

(Robert Quinlan / Alamy)

20. Alaska

Gender pay gap: 19.2%

(retro traveler/Flickr)

19. Delaware

Gender pay gap: 19.0%

(J. Stephen Conn/Flickr)

18. Tennessee

Gender pay gap: 18.5%

(Jim Nix / Nomadic Pursuits/Flickr)

17. Minnesota

Gender pay gap: 18.4%

(kla4067/Flickr)

16. Rhode Island

Gender pay gap: 18.3%

(Dougtone/Flickr)

15. Georgia

Gender pay gap: 18.2%

(Ian Dagnall Commercial Collection / Alamy)

14. Colorado

Gender pay gap: 18.1%

(Jesse Varner/Flickr)

13. Massachusetts

Gender pay gap: 18.0%

(Manu_H/Flickr)

11. Connecticut

Gender pay gap: 17.4%

(Dougtone/Flickr)

10. Vermont

Gender pay gap: 16.2%

(pthread1981/Flickr)

9. Arizona

Gender pay gap: 15.9%

(Photoshot Holdings Ltd / Alamy)

8. California

Gender pay gap: 15.8%

(Robert Landau / Alamy)

7. North Carolina

Gender pay gap: 15.3%

(sevenblock/Flickr)

6. Florida

Gender pay gap: 15.1%

(FL Stock / Alamy)

5. Nevada

Gender pay gap: 14.9%

(D-Stanley/Flickr)

4. Maryland

Gender pay gap: 14.6%

(tim caynes/Flickr)

3. Hawaii

Gender pay gap: 14.1%

(Mauro Ladu / Alamy)

2. New York

Gender pay gap: 13.2%

(drpavloff/Flickr)

1. Washington D.C.

Gender pay gap: 10.4%

(Alexandre Deslongchamps via Getty Images)

Puerto Rico has the smallest gender pay gap, and it benefits women.

Gender pay gap: -4.6% -- Women earn more than men by a small margin

(Fuse via Getty Images)

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In Puerto Rico, meanwhile, women made nearly 5 percent more than men. Nearly half of the island's 3.5 million people live below the poverty line, and the economy has been contracting for most of the past decade.

The report also noted how the wage gap widens with age.

Nationwide, women on the low end of the wage scale ages 65 and up have a median retirement income that is 44 percent less than men, it said.